ARM: omap2plus_defconfig: Enable droid 4 USB PHY

Let's enable this as loadable module for droid 4.

Cc: Marcel Partap <mpartap@gmx.net>
Cc: Michael Scott <michael.scott@linaro.org>
Cc: Sebastian Reichel <sre@kernel.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>